Press arrangement

ABSTRACT

Press arrangement for dewatering a paper, board, tissue or other fibrous web in a machine for producing and/or finishing the same. Arrangement includes only one elongated dewatering nip, through which the fibrous web, having at least one endlessly circulating water-absorbing dewatering belt arranged on each web surface, is led. After the dewatering nip, the fibrous web runs through a smoothing nip. The instant abstract is neither intended to define the invention disclosed in this specification nor intended to limit the scope of the invention in any way.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 10 2004 050 593.4 filed Oct. 16, 2004, the disclosure of which is expressly incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a press arrangement for dewatering a paper, board, tissue or other fibrous web in a machine for producing and/or finishing the same, having only one dewatering nip, which is of extended design and through which, in addition to the fibrous web, on both sides in each case at least one endlessly circulating water-absorbing dewatering belt is led.

2. Discussion of Background Information

Dewatering apparatus of this type is efficient since a relatively high dewatering performance is provided with little requirement for space and expenditure on machinery.

However, the surface properties are not satisfactory, in particular when the fibrous web is also to be coated.

SUMMARY OF THE INVENTION

Therefore, the present invention improves surface properties of the fibrous web with the least possible expenditure.

According to the invention, after the dewatering nip, the fibrous web runs through a smoothing nip.

This smoothing nip reduces the roughness of the fibrous web considerably with relatively little expenditure. In this case, the smoothing is assisted by the relatively high moisture content of the fibrous web and the associated easier deformability.

A constructional simplification results if the dewatering nip is formed by a shoe press roll having a flexible roll shell, which is pressed against a cylindrical mating roll by a pressing element with a concave press surface.

Here, in order to permit careful dewatering by way of a relatively long residence time of the fibrous web in the dewatering nip, the press nip should be at least 300 mm, preferably at least 350 mm, long in the web running direction.

Since the dewatering of the fibrous web is carried out by only one dewatering nip, the dewatering belts must be able to pick up a great deal of water, for which reason heavy or moderately heavy press felts are preferably used.

These dewatering belts have to be dewatered again following the passage of the fibrous web and the discharge of the fibrous web. In order that sufficient time and space remains in particular even at high machine speeds, the dewatering belts must be at least 25 m long. In this case, the dewatering is preferably carried out by a plurality of powerful tubular suction devices.

The dewatering belt running under the fibrous web, after discharging the fibrous web, should wrap around at least one deflection guide roll located in the loop of the dewatering belt, after which the fibrous web runs onward at least with a component counter to the web running direction. During this sharp deflection, the fibrous web or residues thereof are normally already separated from the dewatering belt and fall downward into the pulper.

In order to free the lower dewatering belt of adhesions, after the deflection guide roll, it should wrap around a smooth outer guide roll located outside the loop of this dewatering belt. The contaminants of the dewatering belt are picked up by the smooth circumferential surface of the outer guide roll during contact and are led away via a doctor belonging to the outer guide roll.

In order to simplify the web guidance, the fibrous web, after being led away from the dewatering belts, should run unsupported over a free section as far as the smoothing nip. This also makes it possible to arrange a knock-off device severing the fibrous web as required in the region of the free section. This knock-off device severs the fibrous web in an emergency and in this way prevents web material continuing to be fed to the following machine units, which could lead to damage to the same under certain circumstances.

The severed fibrous web runs into the pulper located underneath it.

In order to simplify the transfer of the fibrous web when starting up the machine, the smoothing nip should be formed by two smoothing rolls with a smooth circumferential surface and, preferably, the lower smoothing roll of the smoothing nip should be movable vertically. In this way, the smoothing nip can be opened simply during the transfer.

After the smoothing nip, the fibrous web should be led to at least one following drying group, in which the fibrous web preferably comes into contact with heated drying cylinders for the purpose of drying and is supported by at least one dryer fabric.

In the drying groups, the fibrous web can be dried on two sides, which can be implemented for example by way of serpentine web guidance over two rows of drying cylinders, each row being assigned a dryer fabric.

However, the fibrous web can also be dried on only one side. In this case, the fibrous web, supported by the dryer fabric, runs in serpentine fashion alternately over heated drying cylinders and guide rolls.

Here, too, the fibrous web can run unsupported between the smoothing nip and the pick-up by the dryer fabric.

However, it can also be advantageous if at least one smooth, endlessly circulating transfer belt is led through the smoothing nip. This permits the transfer belt to transfer the fibrous web to the dryer fabric, which makes the web guidance more secure, in particular at high machine speeds.

It order to simplify the construction, there should be a common pulper under the press arrangement and the start of the first drying group.

Because of the smooth surfaces of the fibrous web, this press arrangement is primarily suitable for applications in which the fibrous web is subsequently also coated. This means that the fibrous web is led through a surface coating apparatus after drying.

Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:

FIG. 1 shows a schematic cross section through a press arrangement with smoothing nip; and

FIG. 2 shows another press arrangement with transfer belt 19.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

In both cases, the fibrous web 1 is transferred from a forming fabric 2 of a former for sheet forming to an endlessly circulating water-absorbing dewatering belt 3 above the fibrous web 1. This transfer is assisted by an evacuated guide roll around which the dewatering belt 3 wraps.

The upper dewatering belt 3 leads the fibrous web 1 to the single dewatering nip of the press arrangement, through which the fibrous web 1 runs together with the upper and a lower, likewise water-absorbing, endlessly circulating dewatering belt 4.

This dewatering nip is of an extended design and is formed by a shoe press roll 6 and a cylindrical mating roll 7. The shoe press roll 6 has a flexible roll shell, which is pressed toward the mating roll 7 by a pressing element 8 with a concave press surface.

The press nip is about 350 millimeters long, which ensures a sufficiently long residence time of the fibrous web 1 in the press nip and permits careful but nevertheless intensive dewatering at a relatively low press pressure.

After the dewatering nip, the upper dewatering belt 3 is led away from the fibrous web 1, so that it is guided only by the lower dewatering belt 4. In order to assist this separation, in this region, the lower dewatering belt 4 runs along a separating suction device 9, whose vacuum reinforces the adhesion of the fibrous web 1 to the lower dewatering belt 4. It may also be advantageous to configure the dewatering belts 3, 4 in such a way that the adhesion of the fibrous web 1 to the lower dewatering belt 4 is stronger than to the upper 3.

The fibrous web 1 is subsequently also separated from the lower dewatering belt 4. From there, it passes over a short free section without guidance by a belt or a roll to the smoothing nip.

The lower dewatering belt 4, after the discharge of the fibrous web 1, is led over a deflection guide roll 13 located in the loop of the dewatering belt 4, around which it wraps to such a great extent that the dewatering belt 4 subsequently runs with at least one component counter to the web running direction 18. This relatively sharp deflection ensures that the fibrous web 1 or parts thereof which are still adhering to the dewatering belt 4 are loosened and fall into the pulper 17 located underneath.

However, in order to free the dewatering belt 4 reliably from adhesions, the lower dewatering belt 4 subsequently wraps around a further outer guide roll 14 located outside the loop. Any adhesions which may be present on the dewatering belt 4 are discharged to the smooth circumferential surface of the outer guide roll 14 and from there are led into the pulper 17 by a doctor 15.

The dewatering belts 3, 4 are designed as heavy press felts because of the necessary high water absorption capacity. In order also to be able to dewater these again sufficiently after the press nip, they are 25 m long. The dewatering is carried out by a plurality of powerful tubular suction devices.

The smoothing nip is formed by two smoothing rolls 11, 12 with a smooth circumferential surface. In order to make the introduction of the fibrous web 1 easier, the lower smoothing roll 12 can be moved vertically. In this way, the smoothing nip can be opened for the transfer. A doctor 21 is assigned to the two smoothing rolls 11, 12.

Above the short free section to the smoothing nip there is a knock-off device 10, which can sever the fibrous web 1. The activation of the device 10 is preferably carried out in the event of a break or tear, so that the feeding of the web into following units is interrupted. This protects the units against damage.

The severed fibrous web 1 runs into the pulper 17.

Following the smoothing nip, the fibrous web 1 passes into one of a plurality of following drying groups for drying.

According to FIG. 1, the fibrous Web 1, after being separated from the upper smoothing roll 11, runs unsupported through a short section before it is picked up by a dryer fabric 5 of the drying group. In order that, in the process, the fibrous web 1 after the smoothing nip runs along together with the upper smoothing roll 11 for at least a short distance, the circumferential surface of the lower smoothing roll 12 is somewhat harder than that of the upper 11.

In the drying group, the fibrous web 1 is dried on both sides. To this end, it wraps in a serpentine fashion around the heated drying cylinders 16 of two rows of drying cylinders arranged one above the other. In this case, each row of drying cylinders is assigned a dryer fabric 5, which presses the fibrous web 1 against the circumferential surface of the drying cylinders 16 of the corresponding row of drying cylinders.

In FIG. 2, a smooth transfer belt 19 belonging to the lower smoothing roll 12 runs through the smoothing nip in addition to the fibrous web 1. This transfer belt 19 is able to lead the fibrous web 1 to the pick-up dryer fabric 5 after the smoothing nip. Here, too, the pick-up can be assisted by a guide roll which is evacuated and around which the air-permeable dryer fabric 5 wraps.

In the following drying group, the fibrous web 1 is dried on only one side. For this purpose, supported by the dryer fabric 5, it runs in serpentine fashion alternately over heated drying cylinders 16 and evacuated guide rolls 20.

For the purpose of simplification, in both cases the pulper 17 extends over the press arrangement and the start of the drying group.

After the drying groups, the fibrous web 1 reaches a coating apparatus, in which the fibrous web 1 can be coated on one or both sides. Because of the smoothness of the fibrous web 1 achieved in the press arrangement having the smoothing nip, coating with very good quality is possible.

It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. 

1. A press arrangement for dewatering a paper, board, tissue or other fibrous web in a machine for producing and/or finishing the same, having only one dewatering nip, which is of extended design and through which, in addition to the fibrous web, on both sides in each case at least one endlessly circulating water-absorbing dewatering belt is led, wherein the fibrous web runs through a smoothing nip after the dewatering nip.
 2. The press arrangement as claimed in claim 1, wherein the dewatering nip is formed by a shoe press roll having a flexible roll shell, which is pressed against a cylindrical mating roll by a pressing element with a concave press surface.
 3. The press arrangement as claimed in claim 1, wherein the press nip is at least 300 mm, preferably at least 350 mm, long in the web running direction.
 4. The press arrangement as claimed in claim 1, wherein the dewatering belts are at least 25 m long.
 5. The press arrangement as claimed in claim 1, wherein the dewatering belt running under the fibrous web, after discharging the fibrous web, wraps around at least one deflection guide roll located in the loop of this dewatering belt, after which the fibrous web runs onward counter to the web running direction.
 6. The press arrangement as claimed in claim 5, wherein the lower dewatering belt, after the deflection guide roll, wraps around an outer guide roll located outside the loop of this dewatering belt.
 7. The press arrangement as claimed in claim 6, wherein the outer guide roll is assigned a doctor.
 8. The press arrangement as claimed in claim 1, wherein the fibrous web, after being led away from the dewatering belts, runs unsupported over a free section as far as the smoothing nip.
 9. The press arrangement as claimed in claim 8, wherein a knock-off device severing the fibrous web as required is arranged in the region of the free section.
 10. The press arrangement as claimed in claim 1, wherein the smoothing nip is formed by two smoothing rolls and the lower smoothing roll of the smoothing nip can preferably be moved vertically.
 11. The press arrangement as claimed in claim 1, wherein, after the smoothing nip, the fibrous web is led to at least one following drying group, in which the fibrous web preferably comes into contact with heated drying cylinders for the purpose of drying and is supported by at least one dryer fabric.
 12. The press arrangement as claimed in claim 11, wherein the fibrous web is dried on two sides in the drying group.
 13. The press arrangement as claimed in claim 11, wherein the fibrous web is dried on one side in the drying group.
 14. The press arrangement as claimed in claim 11, wherein the fibrous web runs unsupported between the smoothing nip and the pick-up by the dryer fabric.
 15. The press arrangement as claimed in claim 1, wherein at least one smooth, endlessly circulating transfer belt is led through the smoothing nip.
 16. The press arrangement as claimed in claim 15, when the transfer belt transfers the fibrous web to the dryer fabric.
 17. The press arrangement as claimed in claim 11, wherein there is a pulper under the press arrangement and the start of the first drying group.
 18. The press arrangement as claimed in claim 1, wherein the fibrous web is led through a coating apparatus after the drying. 